In a cognitive radio system of the type considered for use by IEEE 802-sponsored systems as well as other cognitively-enabled systems under consideration, a cognitive secondary radio system will utilize spectrum assigned to a primary system using an opportunistic approach. With this approach, the secondary radio system will share the spectrum with primary incumbents as well as those operating under authorization on a secondary basis. Under these conditions, it is imperative that any user in the cognitive radio system not interfere with primary users.
A proposed technique for identifying available channels for use by the secondary communication system involves measuring the signal strength of various channels by nodes within the secondary radio system. This information is reported back to a network controller. If the signal strength of any channel is above a predetermined signal level, the network controller prevents secondary devices from transmitting on that channel.
A weakness in the above technique is that for nodes to monitor all possible channels, they must be able to receive and demodulate signals characterized by many differing modulation techniques. For example, a node wishing to transmit within spectrum utilized by television broadcasts will need to be able to receive and demodulate television signals to make sure no television transmissions are taking place. That same node will need to be able to receive and demodulate signals encoded using the 8VSB and DVB-OFDM digital transmissions, legacy NTSC, PAL, and SECAM analog transmissions, secondarily licensed signals such as analog and digital wireless microphone (Part 74) devices, video assist devices, and other protected signals.
Because various modulation techniques will need to be received and demodulated by nodes in a cognitive radio system, expensive hardware and software must be included in these nodes. Thus, while cognitive radio holds the promise of adding additional spectrum for use by users such as public safety, etc., it also has the potential to make radios more expensive. Therefore, a need exists for a method and apparatus for determining appropriate channels for communication within a cognitive radio system that reduces the complexity of nodes required to make such a determination.